1. Field of the Invention
The present invention relates to a discharge cell used for a plate type ozonizer.
2. Description of the Related Art
A discharge cell shown in FIG. 16 is known as one of discharge cells used for plate type ozonizers.
The discharge cell shown in FIG. 16 comprises a couple of low voltage electrodes 1 and 1 acting for a heat sink, a dielectric body unit 2 arranged between the couple of low voltage electrodes 1 and 1, spacers 4, 4 . . . for forming discharge gaps 3 in both sides of the dielectric body unit 2. The dielectric body unit 2 has multilayer structure where a high-voltage electrode 2b intervenes between two glass plates 2a and 2a as a dielectric body. The spacers 4, 4 . . . . includes metal, ceramics, glass, or a resin, and are arranged in predetermined intervals in the direction perpendicular to a direction of gas circulation in the discharge gaps 3.
In a usual plate type ozonizer, it is made to form the discharge cell by making the low voltage electrodes 1 and 1 and dielectric body unit 2 be a module, and by stacking the modules in the thickness direction with making the low voltage electrodes 1 and 1 shared between adjoining modules.
When generating ozone, it is performed to apply a predetermined high voltage to the high voltage electrode 2b in the dielectric body unit 2 with circulating a raw material gas comprising an oxygen gas or a mixed gas including an oxygen gas into the discharge gaps 3 and 3 formed in both sides of the dielectric body unit 2. Since a silent discharge arises in the discharge gaps 3 and 3 by applying a high voltage, the oxygen gas in the raw material gas is ozonized.
In such a discharge cell for a plate type ozonizer, current tendency is to make each gap amount G of the discharge gaps 3 and 3 be small. It is considered that this is because it becomes possible by making each gap amount G of the discharge gaps 3 and 3 be small to highly concentrate the ozone gas since the cooling efficiency of the discharge gaps 3 and 3 increases, it becomes possible to obtain a discharge effect suitable for ozone generation, and it becomes possible to reduce the thickness of the high voltage electrode 2a, and by extension to the thickness of the discharge cell since it becomes possible to simplify the cooling structure of the high voltage electrode 2a by the cooling efficiency in the discharge gaps 3 and 3 increasing.
Then, as for the reduction of each amount G of discharge gaps (hereinafter, a discharge gap amount G), it is mentioned in the laid-open specification of PCT/US/10764 that it is effective to make it be 0.005 inches or less (0.13 mm or less). Actually, also according to the test and analysis by the present inventor et al., it is apparently effective to the generation of high concentration ozone that each discharge gap amount G is 0.4 mm or less, and in particular, 0.2 mm or less.
However, it is not easy to stably realize a minimum discharge gap amount G that is 0.2 mm or less in amass production level.
That is, in order to realize the minimum discharge gap amounts G, the spacers 4, 4 . . . having the thickness that is the same as the discharge gap amounts G are necessary. As described above, metal, ceramics, glass, or a resin is used as the material of the spacers 4, 4 . . . .
In the discharge cell shown in FIG. 16, pressure F in a cell assembly (hereinafter, cell assembly pressure F) is directly applied to the spacers 4, 4 . . . . Hence, if the spacers 4, 4 . . . are made of elastic bodies such as a resin, the magnitude of the gap amounts G of discharge gaps changes with the magnitude of the cell assembly pressure F, and hence it is difficult to stably manage the discharge gap amounts G at a constant value.
If the spacers 4, 4 . . . are made of rigid bodies such as metal, ceramics, or glass, compression in the thickness direction does not arise, and hence predetermined discharge gap amounts G are secured once. But, since the cell assembly pressure F is directly applied to the spacers 4, 4 . . . and the dielectric body unit 2, depending on the magnitude of the cell assembly pressure F, there is a possibility that the minute spacers 4, 4 . . . may be damaged or the glass plates 2a and 2a in the dielectric body unit 2 may be damaged.
In addition, since it is necessary to equally pressurize the whole discharge cell in any cases, it cannot be avoided to upsize a pressurizing mechanism (clamping mechanism).
In addition, in the above-described discharge cell, since the gas circulates in parallel and one-way traffic from the front of the discharge gaps 3 and 3 to the back, it is necessary to take out the ozone gas through a comparatively large header attached in the back face of the discharge cell. For this reason, the ozonizer is further enlarged, and hence manufacturing cost also increases.
Furthermore, in a usual discharge cell, as described above, since the stacked structure where many modules are stacked in the thickness direction is adopted, a laminated face appears in the back face, on which the header is attached, as it is, and hence it is not flat. For this reason, since it is difficult to perform sealing between the discharge cell and header, this sealing cost also increases.
In a discharge cell for an ozonizer, it is important to miniaturize the discharge cell with keeping the same performance, or to enhance performance without upsizing the discharge cell. There are several methods for enhancing the performance, and one of them is to enhance ozone-generating efficiency by suppressing temperature increase in the discharge gaps 3 and 3. For this reason, electrodes, that is, at least the low voltage electrodes 1 and 1 are made to be coolers with jacket structure to entirely cool the discharge gaps 3 and 3 from both sides. There is thinning of a cell module as another method. Supposing the thickness of each module is reduced to one half, cell modules whose number is twice as many as the number of conventional cell modules can be arranged in the same space, and hence performance is enhanced twice.
However, it is difficult to thin a cell module in a conventional discharge cell. A main reason is that the thickness of the cooler is dominant over that of the cell module. Since essentially having large thickness in comparison with other components such as a dielectric body made of a thin plate, the cooler with the jacket structure becomes a major cause of blocking the thinning of the cell module. In addition, since fittings attached to side faces for the supply and exhaust of cooling water mutually interfere, it is difficult to thin the cooler to the thickness smaller than the size of the fittings.
Therefore, since the thickness of the cooler is dominant over the thickness of the cell module, it is difficult to thin the cell module to the thickness smaller than that of the present cell module.
In addition, the number of stacked layers of the cell module is large, for example, 30. For this reason, it has great influence on the price reduction of a discharge cell for an ozonizer to reduce the manufacturing cost of each module. As for the high voltage electrode 2b intervening between the two glass plates 2a and 2a in the dielectric body unit 2, it is known that cooling becomes unnecessary by thinning. From this viewpoint, the high voltage electrode 2b is formed by integrally coating a conductive material over both surfaces of the glass plates 2a and 2a by metallizing, plating, thermal spraying, or the like.
Owing to this, since a gap is eliminated from between the glass plate 2a and high voltage electrode 2b, a discharge required for generating ozone stably arises in the discharge gap 3. However, on the other hand, since coating cost for forming an electrode increases, this becomes a major factor of increasing the manufacturing cost of each module. In addition, it is also a problem that mechanical and physical secondary abuses arise and leading of a terminal area becomes difficult, by the glass plate 2a being heated in the coating process.
In addition, conventionally, this high-voltage electrode 2b is formed with coating substantially over the glass plates 2a and 2a, and the depth of the high voltage electrode 2b in the fore-and-aft direction is substantially the same as the depth of the low voltage electrodes 1 and 1 with the depth of the glass plates 2a and 2a. Nevertheless, as a recent tendency, the thickness of the glass plate 2a has been made thin so as to miniaturize a discharge cell, and the distance between components of the discharge cell is shortened. Hence, it has become impossible to secure the sufficient insulation distance between the high voltage electrode 2b and low voltage electrodes 1 and 1. For this reason, since unusual discharges frequently occur between the high voltage electrode 2b and low voltage electrodes 1 and 1, the deterioration of reliability of the discharge cell has been a problem.
An object of the present invention is to provide a discharge cell for an ozonizer that can stably secure the minimum discharge gap amount G such as 0.2 mm or less in a mass production level, and can avoid the breakage of a cell component and the upsizing of a pressurizing mechanism (clamping mechanism).
Another object of the present invention is to provide a small and economical discharge cell for an ozonizer where it is easy to exhaust ozone gas in spite of performing gas circulation in a parallel flow.
Still another object of the present invention is to provide a discharge cell for an ozonizer that has a thin cooler without lowering coolability, and makes it possible to drastically enhance performance.
Further another object of the present invention is to provide an economical discharge cell for an ozonizer that can reduce the manufacturing cost of a module, and in particular, electrode formation cost.
Still further another object of the present invention is to provide a discharge cell for an ozonizer with high reliability that does not cause an unusual discharge.